The present invention relates to a method for error detection during charging of an energy storage system in a vehicle, said vehicle comprising an electric machine which is arranged for propulsion of said vehicle, said method comprising: requesting a charging pattern from an external power supply by means of a vehicle control unit, upon connection of said energy storage system to said external power supply; and supplying said charging pattern to said energy storage system by means of an external charging control unit forming part of said external power supply.
The invention also relates to an arrangement for error detection during charging of an energy storage system in a vehicle with an electric machine arranged for propulsion of said vehicle, said arrangement further comprising a vehicle control unit arranged for requesting as charging pattern from an external power supply upon connection of said energy storage system to said external power supply; and wherein the external power supply comprises an external charging control unit arranged for supplying said charging pattern to said energy storage system.
In the field of vehicles, there is a steady increase in research and development related to propulsion of vehicles with alternative power sources, i.e. power sources being used as alternatives to conventional internal combustion engines.
An internal combustion engine, for example in the form of a gasoline engine or a diesel engine, offers high efficiency with relatively low fuel consumption. However, environmental concerns have led to an increase in development of more environmental-friendly power sources for vehicles. In particular, the development of electrically operated vehicles has emerged as a promising alternative.
Today, there exist various types of vehicle propulsion systems comprising electric machines. For example, a vehicle can be operated by means of an electric machine solely, or by means of an arrangement comprising both an electric machine and an internal combustion engine. The latter alternative is often referred to as a hybrid electric vehicle (HEV), and can for example be utilized in a manner in which an internal combustion engine is used for operating the vehicle while driving outside urban areas whereas the electric machine can be used in urban areas or in environments in which there is a need to limit the discharge of harmful pollutants such as carbon monoxide and oxides of nitrogen.
The technology involved in electrically operated vehicles is closely related to the development of electrical energy storage systems, for example in the form of battery-related technology for vehicles. Today's electrical energy storage systems for vehicles may comprise a set of rechargeable battery cells which, together with control circuits, forms a unit which is arranged in a vehicle and which is configured for operating an electric machine. A hybrid vehicle is also often arranged so that the energy storage system is charged during braking, by means of a process known as regenerative braking.
A vehicle being operated by means of an internal combustion engine and an electric machine supplied with power from a rechargeable electrical energy storage system is sometimes referred to as a plug-in hybrid electric vehicle (PHEV). A plug-in hybrid electric vehicle uses an energy storage system with rechargeable batteries or another suitable energy source which can be restored into a condition involving a full charge through a connection to an external electric power supply.
The external power supply can be in the form of the common electric grid power system which can be accessed via a conventional power cord, or can be in the form of other arrangements depending on the vehicles involved and the power need for the recharging process. In case of vehicles in the form of buses or heavy transport vehicles, more powerful charging devices and procedures are normally needed as compared with smaller cars and similar vehicles.
A challenge for today's electrically driven vehicles, in particular heavy vehicles such as buses and trucks, is that a high amount of energy must be charged into the energy storage system in a relatively short time in order to optimize the vehicle's range of driving. For this reason, the actual charging of the energy storage system is suitably implemented through a process in which a control unit on the vehicle requests a charging to be carried out by means of an external electric power supply. This is carried out after the energy storage system and the external power supply have been electrically connected by means of suitable connector elements. In such cases, a so-called pantograph can for example be used to connect the onboard energy storage system with an external power supply.
The recharging of an energy storage system in a bus, for example, may involve charging an electrical energy storage system comprising a number of battery cells with a charging current which is of the magnitude 200 A, whereas the electrical energy storage system may have a voltage of the magnitude of 600 V. Such a charging procedure involves certain safety risks, for example if the battery cells are exposed to excessive heat, impact or overcharging, or if electrically conducting parts of the energy storage system or charging system come into contact with persons. Consequently, there are demands for protection of persons in the event of any error which may occur during charging.
Also, the battery cells of the energy storage system are both very expensive and also very sensitive to overcharging. This also means that overcharging of the energy storage system must not occur.
The patent document US 2011/196545 teaches a charging system for a hybrid vehicle in which a power storage device is charged by means of a power supply. If the vehicle in question should move during charging, a control unit stops the charging process. Said control unit then diagnoses a state of the charging unit and resumes the charging when this is possible.
Even though the above-mentioned solution according to US 2011/196545 offers a reliable solution for terminating the charging process if the vehicle should move, there are still further demands for a sufficiently high level of safety for persons and for electric equipment during charging of an energy storage system, in particular in hybrid vehicles.
It is desirable to provide an improved method and arrangement by means of which the above-mentioned problems can be overcome and, in particular, by means of which any errors occurring during charging of an energy storage system in a vehicle can be detected in an effective and secure manner. Such detection can then be used for discontinuing the charging process or for issuing an alarm signal.
In accordance with an aspect of the invention, a method is provided for error detection during charging of an energy storage system in a vehicle, said vehicle comprising an electric machine which is arranged for propulsion of said vehicle. The method comprises requesting a charging pattern from an external power supply, by means of a vehicle control unit, upon connection of said energy storage system to said external power supply, and supplying said charging pattern to said energy storage system by means of an external charging control unit forming part of said external power supply. Furthermore, said method comprises: providing a predetermined modulation of the requested charging pattern; evaluating whether the charging pattern supplied to said energy storage system comprises said predetermined modulation; and, if this is not the case, indicating that the charging of said energy storage system is erroneous.
By means of the invention, there is provided a safe and reliable method for determining whether any unexpected error in the charging of the energy storage system occurs, and for terminating the charging and issuing at alarm in the event such an error occurs.
A particular advantage of the invention is that the request for the charging pattern can be transmitted through a transmission path from the vehicle to the external power supply, after which the vehicle control unit may determine, during said evaluation step, whether the charging pattern which is actually received by the vehicles energy storage system also corresponds to the requested charging pattern.
According to an embodiment, the modulation is provided for example in the form of a predetermined, temporary change of frequency, amplitude or wave shape of a charging current which is supplied through said charging pattern. This means that the control unit of the vehicle may detect whether this temporary change of for example frequency or amplitude also occurs in the actual charging current. If this is the case, the charging is operating correctly.
Alternatively, the above-mentioned modulation can be provided in the form of an added signal component which is temporarily superimposed to a charging current which is supplied through said charging pattern.
According to an embodiment, an alarm signal is issued in the event that the charging is erroneous. This means that an operator or a driver of the vehicle may activate an emergency switch in the external power supply so as to prevent the energy storage system from being damaged or to prevent any personal injuries. Also, the energy storage system can be disconnected from the external power supply in an automatic manner in case the charging is erroneous. Such disconnection can be made automatically by means of a disconnector unit associated with the vehicles control unit.
According to an embodiment, the information between the control unit on the vehicle and the external power source can be provided on a wireless connection between said hybrid control unit and said external charger control unit.
According to another aspect of the invention, an arrangement is provided for error detection during charging of an energy storage system in a vehicle with an electric machine arranged for propulsion of said vehicle, said arrangement further comprising as vehicle control unit arranged for requesting a charging pattern from an external power supply upon connection of said energy storage system to said external power supply; and wherein the external power supply comprises an external charging control unit arranged for supplying said charging pattern to said energy storage system. According to the invention, the hybrid control unit comprises a modulation unit for applying a predetermined modulation of said requested charging pattern and an evaluation unit for determining whether the charging pattern supplied to said energy storage system comprises said predetermined modulation; and, if this is not the case, indicating that said charging of said energy storage system is erroneous.
The invention is particularly adapted for being used in a so-called plug-in hybrid vehicle, having an internal combustion engine and an electric machine which are arranged for propulsion of said vehicle.
The term “charging pattern” refers to a predetermined schedule, sequence or progression of the recharging process. Such a charging pattern can for example be in the form of a “quick charge”, i.e. involving a relatively high charging current during a relatively short time period, or a “standard charge”, i.e. involving a lower charging current during a relatively long time period. A charging pattern of the “quick charge” type can for example be suitable for recharging the energy storage system of a bus while the bus is being parked briefly during a lunch break or between two consecutive rounds. Consequently, a “charging pattern” is a charging sequence with a certain charging current and voltage which occurs for a certain time or until a certain state of charge has been achieved by the energy storage system
Furthermore, the term “modulation” refers to any predetermined variation, deviation or adaptation of the charging current or charging voltage which can be controlled by the vehicles control unit and requested to be supplied from the external power supply. Such a “modulated” charging pattern can subsequently be detected and evaluated by the vehicles control unit in order to determine whether the charging supplied by the external power supply corresponds to the requested charging. Any difference between the requested charging pattern and the supplied charging pattern can be interpreted as an error of the charging process.